The defect chemistry and charge transport properties of La_0.95Sr_0.05Ga_0.95Mg_0.05O_3-δ (LSGM) single crystals, grown by the Czochralski technique, were studied by impedance spectroscopy performed over a wide temperature range (180–800°C) and oxygen partial pressures from 0.21 to 1013 mbar. Owing to ion blocking Pt thin film electrodes impedance data showed a Warburg type 45° slope in the complex impedance plane. The spectra were analyzed by means of a generalized transmission line model which yielded the electronic and ionic conductivity, chemical and dielectric capacitance and the oxygen chemical diffusion coefficient. Activation energies for electronic (0.89 eV) and ionic charge transport (0.95 eV at low and 0.56 eV at high temperatures) were determined. Oxygen partial pressure dependent measurements revealed that the p-type conductivity is exactly proportional to pO₂^1/4 and that the ionic transference number approaches 1 for low oxygen partial pressures and low temperatures. Additional Hebb-Wagner type DC polarization experiments were carried out to determine the n- and p-type conductivities in a broad chemical potential range and to verify the results obtained by the AC impedance measurements.

Optical absorption spectra and luminescence spectra were recorded as a function of temperature between 295 K and 800 K for single crystal samples of Gd₂SiO₅:Dy³⁺, Lu₂SiO₅:Dy³⁺, LiNbO₃:Dy³⁺, and Gd₃Ga₃Al₂O₁₂:Dy³⁺ fabricated by the Czochralski method and of YAl₃(BO₃)₄:Dy³⁺ fabricated by the top-seeded high temperature solution method. A thermally induced change of fluorescence intensity ratio (FIR) between the ⁴I_15/2→ ⁶H_15/2 and ⁴F_9/2 → ⁶H_15/2 emission bands of Dy³⁺ was inferred from experimental data. It was found that relative thermal sensitivities S_R at 350 K are higher for YAl₃(BO₃)₄:Dy³⁺ and Lu₂SiO₅:Dy³⁺than those for the remaining systems studied. Based on detailed examination of the structural peculiarities of the crystals it was ascertained that the observed difference between thermosensitive features cannot be attributed directly to the dissimilarity of structural factors consisting of the geometry and symmetry of Dy³⁺ sites, the number of non-equivalent Dy³⁺ sites, and the host anisotropy. Instead, it was found that a meaningful correlation between relative thermal sensitivity S_R and rates of radiative transitions of Dy³⁺ inferred from the Judd–Ofelt treatment exists. It was concluded that generalization based on the Judd–Ofelt parameters and luminescence branching ratio analysis may be useful during a preliminary assessment of thermosensitive properties of new phosphor materials.